Accessory drive for driving a balance shaft

ABSTRACT

Engines may be provided with one or more balance shafts to provide a balancing effect to the engine during operation. Normally, the balance shafts are located where they can be driven by the engine&#39;s front end drive assembly. However, driving balance shafts or any other engine accessory off the front end drive assembly has implications in respect of both increased engine noise and extended engine length. An engine accessory drive in accordance with the present invention reduces engine noise and engine length while providing a balancing effect. An engine accessory drive includes a primary drive ( 7 ) drivable by the crankshaft ( 9 ) of the engine and a rotary member ( 5 ) such as a drive pulley mounted on a drive shaft ( 27 ) which is drivable by the primary drive ( 8 ).

TECHNICAL FIELD

[0001] This invention relates to an accessory drive for driving abalance shaft, to an engine including the balance shaft, and to a methodof driving a balance shaft.

BACKGROUND

[0002] It is known to provide engines with one or more balance shafts toprovide a balancing effect for the engine when in operation. Normally,such balance shafts are positioned on the engine where they can bedriven by the engine's front end drive assembly. As a result, the enginedesigner is restricted as regards where the balance shafts can belocated. Furthermore, the overall length of the engine is dictated bythis conventional arrangement, with the result that a designer haslimited scope for reducing engine dimensions and/or weight.

[0003] The present invention sets out to overcome these and otherdisadvantages of the prior art.

SUMMARY OF THE INVENTION

[0004] According to the invention there is provided an engine accessorydrive comprising a primary drive drivable by a crankshaft of the engine,a rotational member mounted on a drive shaft drivable by the primarydrive, a secondary drive external of the engine and drivable by therotational member, and at least one engine accessory drivable by thesecondary drive, the at least one engine accessory including a balanceshaft.

[0005] According to the invention there is also provided an enginecomprising a crankshaft, a primary drive drivable by the crankshaft, arotational member mounted on a drive shaft drivable by the primarydrive, a secondary drive drivable by the rotational member, and at leastone engine accessory drivable by the secondary drive, the at least oneengine accessory including a balance shaft.

[0006] According to the invention there is also provided a method ofdriving an engine accessory comprising the steps of providing an enginewith a crankshaft, driving a primary drive from the crankshaft, drivinga drive shaft from the primary drive, the drive shaft having arotational member mounted thereon, driving a secondary drive from therotational member, and driving at least one engine accessory from thesecondary drive, the at least one engine accessory including a balanceshaft.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying diagrammatic drawings,in which:

[0008]FIG. 1 is an isometric view of an engine having an accessory drivefor driving a balance shaft in accordance with the invention, and

[0009]FIG. 2 is an isometric view of the accessory drive and accessoriesof the engine of FIG. 1.

DETAILED DESCRIPTION

[0010]FIG. 1 shows an engine 1 having a front end 2 and a rear end 3.The front end 2 is provided with an accessory or secondary drive 4 inaccordance with the invention and shown in more detail in FIG. 2.

[0011] In the illustrated embodiment the accessory drive 4 is made up ofa drive pulley 5 and a belt 6 in communication with the drive pulley 5so that the belt 6 is driven by the drive pulley 5. It is to beunderstood that any flexible continuous drive member 6 may be used inplace of a belt, such as a chain (not illustrated).

[0012] The drive pulley 5 is mounted on a drive shaft 27 which in turnis driven by a primary drive in the form of a chain drive 7 within theengine 1. Alternatively, chain drive 7 may be a belt drive, a geardrive, or any other conventional drive. The drive pulley 5 may bereplaced by any suitable rotational member.

[0013] The chain drive 7 is made up of a drive chain 8, a crankshaftsprocket 10 mounted on a crankshaft 9 towards the front end 2 of theengine 1, an idler sprocket 11 and a camshaft sprocket 12 mounted on acamshaft 13 at the front end 2 of the engine 1. The drive chain 8extends between the crankshaft sprocket 10, the idler sprocket 11, thecamshaft sprocket 12 and a drive sprocket 14 to drive the drive pulley5.

[0014] More particularly, the drive sprocket 14 is disposed on the driveshaft 27 which is in turn in direct communication with a common railfuel pump 26 so that rotation of the drive sprocket 14 results inrotation of the drive shaft 27 to drive a common rail fuel pump 26.Accordingly, the common rail fuel pump 26 is driven by the crankshaft 9via the chain drive 7. The drive pulley 5 is therefore drivensimultaneously with the common rail fuel pump 26. Typically, the commonrail fuel pump 26 is driven at faster than engine speed e.g. up to oneand a half times or twice engine speed. The drive shaft 27 has an axisof rotation which is offset from the axis of rotation of the crankshaft9.

[0015] As will be appreciated by those skilled in the art, the commonrail fuel pump 26 is optional and the drive shaft 27 could be incommunication with an alternative accessory type or a stand-alone shaft.However, in general, the drive shaft 27 is rotatable at engine speed orgreater.

[0016] The common rail fuel pump 26 can be any other accessory e.g. analternator, fan, power steering pump, air conditioning pump, oil pump orthe like.

[0017] A rotary seal is provided on the drive shaft 27 between theengine 1 and the drive pulley 5 at a location generally indicated by thereference numeral 31 to prevent engine oil leakage or dirt ingress.

[0018] Drive from the crankshaft 9 is transmitted to the drive pulley 5via the drive chain 8 to drive the belt 6 which can in turn drive engineaccessories as shall be explained more fully below.

[0019] Preferably, the primary chain drive 7 is located within theengine 1 while the secondary accessory drive 4 is located substantiallyexternally of the engine 1.

[0020] In the present embodiment of the invention, the engine 1 isprovided with engine accessories in the form of first and second tubularbalance shafts 15, 16 externally mounted on the engine 1. The balanceshafts 15, 16 are offset vertically with respect to a centreline 17 ofthe crankshaft 9 i.e. the balance shaft 16 is set lower than thecentreline 17 of the crankshaft 9 and the balance shaft 15 is set higherthan the centreline 17. A balance shaft design that may be used withthis invention is illustrated in commonly-owned British PatentApplication No 0106852.7 filed on Mar. 20, 2001.

[0021] The crankshaft 9 is covered by a crankshaft cover plate 18 toenclose the crankshaft 9.

[0022] The drive pulley 5 is disposed adjacent the first balance shaft15 above the centreline 17.

[0023] A further front end engine accessory in the form of an alternator19 is disposed over the second balance shaft 16 on the engine 1 and isprovided with an alternator pulley 20 for receiving the belt 6. Thefirst and second balance shafts 15, 16 are provided with first andsecond balance shaft pulleys 21, 22 respectively in communication withthe belt 6 to drive the first and second balance shafts 15, 16.

[0024] The belt 6 is a synchronous belt having teeth 23 on a top face 24and a bottom face 25 thereof. The belt 6 extends between the drivepulley 5, the alternator idler pulley 20, the first balance shaft pulley21 and the second balance shaft pulley 22 so that the drive pulley 5 caneffect contra-rotation of the first and second balance shafts 15, 16 viathe belt 6.

[0025] At least the drive pulley 5 and the balance shaft pulleys 21,22are synchronous drive pulleys to ensure correct rotational phasing ofthe balance shaft rotational elements (not shown) in relation to thephase angle of the crankshaft 9.

[0026] The effective diameters of the pulleys are configured such thatthe crankshaft 9, via the internal chain drive 7 and drive pulley 5,drives the first and second balance shafts 15, 16 at twice engine speedand the alternator 19 at an appropriate design speed.

[0027] Selection of a drive shaft 27 rotatable at engine speed orgreater reduces the speed step-up required to rotate the balance shafts15,16 at twice engine speed (which speed would be required in an in-linefour-cylinder engine for correct functioning of the balance shafts),therefore the driving load transmitted by belt 6 will be correspondinglylower than if shaft 27 is rotatable at less than engine speed. As anexample, the camshaft 13 is rotatable at half engine speed in afour-stroke engine and is therefore unlikely to be suitable as the driveshaft for drive pulley 5 since a large speed step-up would be required.

[0028] In the present embodiment of the invention the front end 2 of theengine is also provided with a bottom idler pulley 28 below the secondbalance shaft 16 to ensure a peripheral engagement of the belt 6 withthe balance shaft pulley 22 which is sufficient to transfer the drivingforce. The alternator 19 is optional and the alternator pulley 20 cansimply be an upper idler pulley 20.

[0029] As indicated above, the belt 6 is a double-sided synchronous(toothed) belt so that the belt 6 can engage with complementary pulleyteeth 30 on at least the first balance shaft pulley 21, second balanceshaft pulley 22 and the drive pulley 5.

[0030] It will be appreciated by those skilled in the art that anynumber of front end accessories may be driven by the belt 6 via suitablepulleys.

[0031] Industrial Applicability

[0032] The invention finds application in machines where improved noisereduction and reduced vibration is required. The invention also providesthe opportunity to improve engine oil sealing and reduce engine length.

[0033] The primary drive can be substantially contained within theengine while the accessory drive 4 can be external to the engine 1.Accordingly, as the drive for the engine accessories is taken from thedrive pulley 5 via the belt 6, no conventional external drive isrequired to be taken directly from the front end of the crankshaft 9 onthe engine 1. Accordingly, noise and vibration in the engine 1 of theinvention is reduced. It is estimated that the reduction in noise can beas much as 25% or greater over engines having a conventional front enddrive assembly. In addition, no rotary seal is required at the front endof the crankshaft 9.

[0034] An engine 1 having balance shafts 15,16 driven as previouslydescribed can also be made shorter in the longitudinal direction ascompact gearing and sealing arrangements can be employed to drive thebalance shafts 15, 16. Such a reduction in length can providesignificant cost advantages and advantages in designing and manufactureof the engine 1.

[0035] The reduction in length of the engine is further facilitated dueto the absence of mechanical linkages at the front end or nose of thecrankshaft 9 so that the crankshaft cover plate 18 can be provided withits own seal or accessories mounted on the crankshaft nose can beprovided with their own seals which can be more compact than sealsnormally required between mechanical linkages at the nose of thecrankshaft 9.

[0036] The rotary seal provided on the sprocket shaft 27 ensures sealingof the engine 1.

[0037] Moreover, as the nose of the crankshaft 9 is liberated, the noseis made available for driving other engine accessories if required e.g.AC/DC generators, hydraulic pumps, compressors, engine speed generators,transfer gear boxes and the like.

[0038] In addition, where the engine 1 is provided with first and secondbalance shafts 15, 16 as hereinbefore described, the engine can have alighter weight than conventional engines fitted with balance shaftsdriven by mechanical linkages at the nose of the crankshaft 9.

[0039] It is envisaged that the balance shafts 15, 16 could be mountedexternally of the engine 1, but suspended underneath an oil sump 29 tobe below the crankshaft 9. Such an arrangement allows the width of theengine 1 to be reduced (where the engine 1 is being used to power amachine, the width of the engine 1 can be critical as turning of thefront wheels of the machine for steering can cause the wheels to engagethe engine 1).

[0040] Although the balance shafts 15, 16 are shown as being integralwith the engine 1, they need not be, and could be mounted on a flangecast onto the engine block. As the balance shafts 15, 16 are driven bythe accessory drive 4, an engine designer has a greater freedomregarding location of the balance shafts 15, 16 on the engine 1. Thus,the designer can take into account the space that is available andselect a position that provides optimum balancing effect as the balanceshafts 15, 16 do not require to be placed where they must engage withthe gearing of the front end drive assembly.

[0041] The belt 6 can also be directed using idler pulleys tosubstantially any configuration.

[0042] In an alternative embodiment of the invention, the balance shafts15, 16 can be in communication with additional engine accessories at therear end 3 of the engine 1 to facilitate transfer of the drive from theaccessory drive to the additional engine accessories at the rear end.

[0043] Modifications and improvements may be made to the foregoingwithout departing from the scope of the present invention.

1. An engine accessory drive comprising: a primary drive driveable by acrankshaft of the engine, a rotational member mounted on a drive shaftdriveable by the primary drive, the drive shaft having an axis ofrotation offset from the axis of rotation of the crankshaft, a secondarydrive external of the engine and driveable by the rotational member, andat least one engine accessory driveable by the secondary drive, the atleast one engine accessory including a balance shaft.
 2. An engineaccessory drive as claimed in claim 1 wherein the at least one engineaccessory includes first and second balance shafts arranged forcontra-rotation at twice engine speed.
 3. An engine accessory drive asclaimed in either claim 1 or claim 2 wherein the secondary driveincludes a flexible continuous drive member.
 4. An engine accessorydrive as claimed in any preceding claim wherein the secondary driveincludes a synchronous drive belt.
 5. An engine accessory drive asclaimed in any preceding claim wherein the drive shaft is rotatable atengine speed or greater.
 6. An engine accessory drive as claimed in anypreceding claim wherein the primary drive includes a drive selected fromthe group comprising: a belt drive; a chain drive; and a gear drive. 7.An engine comprising: a crankshaft, a primary drive driveable by thecrankshaft, a rotational member mounted on a drive shaft driveable bythe primary drive, the drive shaft having an axis of rotation offsetfrom the axis of rotation of the crankshaft, a secondary drive driveableby the rotational member, and at least one engine accessory driveable bythe secondary drive, the at least one engine accessory including abalance shaft.
 8. An engine as claimed in claim 7 wherein the at leastone engine accessory includes first and second balance shafts arrangedfor contra-rotation at twice engine speed.
 9. An engine as claimed ineither claim 7 or claim 8 wherein the secondary drive includes aflexible continuous drive member.
 10. A method of driving an engineaccessory comprising the steps of: providing an engine with acrankshaft, driving a primary drive from the crankshaft, driving a driveshaft from the primary drive, the drive shaft having a rotational membermounted thereon, driving a secondary drive from the rotational member,and driving at least one engine accessory from the secondary drive, theat least one engine accessory including a balance shaft.
 11. A method asclaimed in claim 10, wherein the drive shaft rotates at a speed ofrotation greater than or equal to the speed of rotation of thecrankshaft.